Retarding control apparatus

ABSTRACT

A retarding control apparatus for controlling operation of a retarder, which is connected to an automatic transmission, by operating a retarder actuating device by manipulation of a retarder changeover switch includes control unit, to which are inputted a shift position signal,a throttle opening signal and a changeover signal from the retarder changeover switch, for outputting an operating signal to the retarder actuating device. When the control unit receives the changeover signal from the retarder changeover switch for actuating the retarder and decides that a manual downshift has taken place based upon the shift position signal and throttle opening signal, the control unit diminishes the operating signal to the retarder actuating device in such a manner that braking force produced by the retarder is reduced by a prescribed value.

This application is a divisional of application Ser. No. 08/183,790,filed Jan. 21, 1994, U.S. Pat. No. 5,352,444, which is a continuation ofapplication Ser. No. 07/660,558, filed Feb. 25, 1991, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a retarding control apparatus operated by amanual changeover. More particually, the invention relates to aretarding control in which braking force due to a retarder is controlleddepending upon the state of a manual shift or the steering angle of awheel and slipping state.

2. Related Art

Relating to a first aspect of the present invention, a heavy vehicleoften is equipped with an auxiliary brake such as an exhaust brake orhydraulic retarder in addition to a foot brake as braking means.

FIG. 1 illustrates an example of a conventional retarding controlapparatus equipped with a hydraulic retarder. When a manually operatedchangeover swich 1 is turned on, an ECU 2 to which a changeover signalfrom the changeover switch 1 is applied outputs a current to a solenoid3 to actuate a control valve 4 and introduce hydraulic pressure to ahydraulic retarder 5, whereby a braking force resulting from theretarder 5 is generated.

First Problem to be Solved by the Invention

In this conventional retarding control apparatus described above,braking force produced by the retarder 5 is regulated by operating thechangeover switch 1. Consequently, in a case where the retarding controlapparatus is combined with an automatic transmission, a braking forceresulting from engine braking accompanying a manual downshift is addedto the braking force produced by the retarder 5 if the manual downshiftis performed by operation of a shift lever when the changeover switch 1is on and the retarder 5 is operating. As a result, the braking force isexcessive and, as indicated by the dashed line in FIG. 7(e),transmission shock at shifting is enlarged by a sudden change in vehiclespeed and deceleration, and driving comfort suffers as a consequence.

Relating to a second aspect of the present invention, FIG. 2 illustratesan example of another retarding control apparatus of a hydraulicretarder 12 mounted on a large-size vehicle 11. When a retarder switch13 provided at the driver's seat of the vehicle 11 is turned on, acontrol valve 15 is actuated by stepping down on a brake pedal 14, andhydraulic pressure acting upon a controller valve 16, which delivershydraulic pressure to the retarder 12, is regulated as a result, therebyeffecting control of braking force by the retarder 12.

Second Problem to be Solved by the Invention

The relationship between coefficient of friction μ, which is producedbetween the tire and the road surface, and slip rate S is as shown inFIG. 3. The effective range of the slip rate S for stable travel is theinterval x in FIG. 3. When the interval x is exceeded, the coefficientof friction μ suddenly declines and the tire skids. Consequently, evenif the vehicle is equipped with ABS (an antiskid braking system), thebraking force of the retarder 12 becomes excessive and there is thedanger that the wheels will lock. The upper limit of the retarderbraking force F for which the wheels will not lock in an instance wherethe effective range of the slipping rate is exceeded is as indicated bythe broken lines y in FIG. 4. The retarder braking force characteristicin FIG. 4 illustrates a case in which the lower the characteristic curvein FIG. 4, the greater the amount the brake pedal 14 is depressed.

In the conventional retarding control apparatus of the kind describedabove, the braking force of the retarder 12 is controlled by regulatingthe amount by which the brake pedal 14 is depressed. Consequently, whenthe slip rate S increases at the time of cornering or at braking on aslippery road surface, there is the danger that the wheels will lock dueto excessive braking. This is extremely dangerous.

In particular, in case of a heavy, large-size vehicle having a longwheel base, the slip rate of the tires is increased by the inner-wheeldifference between the front and rear wheels at cornering, and hence theinfluence of excessive braking becomes especially large and the vehiclebody assumes an unstable state due to locking of the wheels. This can bevery hazardous. The same situation can arise even in a vehicle equippedwith an ABS.

SUMMARY OF THE DISCLOSURE

A general object of the present invention is to provide a retardingcontrol apparatus which solves the aforementioned problems encounteredin the conventional retarding control apparatus.

More specifically, a first object of the present invention is to providea retarding control apparatus in which optimum braking forcecommensurate with the traveling state of the vehicle can be obtainedeven if a retarder operated by a manual changeover switch is used incombination with an automatic transmission.

A second object of the present invention is to provide a retardingcontrol apparatus in which there is no risk of excessive application ofretarder braking force when the vehicle is braked at cornering.

In order to attain the first object in the first aspect of the presentinvention, there is provided a retarding control apparatus forcontrolling operation of a retarder, which is connected to an automatictransmission, by operating a retarder actuating device by manipulationof a retarder changeover switch, characterized by comprising sensingmeans for sensing shift position of a shift lever, throttle openingdetecting means, and control means, to which are inputted a shiftposition signal from the shift position sensing means, a throttleopening signal from the throttle opening detecting means, and achangeover signal from the retarder changeover switch, for outputting anoperating signal to the retarder actuating device, wherein when thecontrol means receives the changeover signal as an input from theretarder changeover switch for actuating the retarder and decides that amanual downshift has taken place based upon the shift position signaland throttle opening signal, the control means diminishes the operatingsignal to the retarder actuating device in such a manner that brakingforce porduced by the retarder is reduced by a prescribed value.

The retarding control apparatus according to the first aspect is suchthat when the retarder changeover signal for operating the retarder isinputted to the control means in response to turn-on of the retarderchangeover switch, the operating signal is outputted to the retarderactuating device so that a prescribed optimum braking force produced bythe retarder is generated.

When the retarder changeover switch is thus turned on and braking by theretarder is taking place, the output of the operating signal to theretarder actuating device is reduced by a prescribed value if the shiftlever is operated and the control means decides that a manual downshifthas occurred based upon input of the shift position signal from theshift position sensing means and the throttle opening signal from thethrottle opening detecting means. Accordingly, at the time of a manualdownshift, the braking force of the retarder is decreased by an amountcommensurate with the reduction in the operating signal.

In a retarding control apparatus which is a variant of the first aspect,the above-described arrangement is supplemented by an arrangementwherein the value of the decrease in the braking force of the retarderat the time of manual downshift by the control means is set incorrespondence with the shift position that prevails after the manualdownshift. As a result, the reduction in the braking force of theretarder at manual downshift is set for every shift position aftermanual downshift so that control of the retarder braking force can beperformed in conformity with each manual downshift.

In accordance with a further modified variant of the first aspect, theretarding control apparatus has vehicle speed detecting means, whereinthe control means, based upon a vehicle speed signal from the vehiclespeed detecting means, sets a time for diminishing the operating signalto the retarder actuating device. This makes it possible to performcontrol of the retarder braking force commensurate with the prevailingvehicle speed.

In accordance with the first aspect described above, the braking forceof the retarder connected to the automatic transmission decreases when amanual downshift is performed. As a result, the braking force actingupon the vehicle owing to the braking force of engine braking thataccompanies a manual downshift is no longer in danger of becomingexcessive. Consequently, transmission shock is mitigated and the feel ofthe ride can be imporved.

In order to attain the second object in the second aspect of the presentinvention, there is provided a retarding control apparatus forcontrolling operation of a retarder, which is connected to an automatictransmission, by operating a retarder actuating device by manipulationof a retarder changeover switch, characterized by:

comprising vehicle speed detecting means for detecting vehicle speed,driving-wheel velocity detecting means for detecting velocity of adriving wheel, steering angle detecting means for detecting steeringangle of a wheel, brake actuation detecting means for detectingactuation of a brake, and control means to which are inputted a vehiclespeed signal, a driving-wheel velocity signal, a steering angle signaland a brake actuation signal from these detecting means and an ON signalfrom the retarder switch, for outputting a retarder operating signal tothe retarding actuating device,

the control means having a map in which are set control characteristicssuch that when slip rate of the wheel is not more than a fixed value,retarder braking force is increasingly reduced the larger slip ratebecomes; when slip rate exceeds the fixed value and lies in apredetermined range, the retarder braking force is held at a constantvalue; and when slip rate exceeds the predetermined range, the retarderbraking force is increasingly reduced the larger the slip rate becomesand is made relatively smaller the larger the steering angle of thewheel becomes,

wherein when the brake actuation signal and the ON signal from theretarder switch are being inputted to the control means, the controlmeans selects from the map, on the basis of the steering angle signal, acontrol characteristics of retarder braking force corresponding tosteering angle, computes slip rate based upon the vehicle speed signaland driving-wheel velocity signal, and outputs the retarder operatingsignal to the retarder actuating device based upon the computed sliprate and the selected control characteristic of the retarder brakingforce.

The retarding control apparatus according to the second aspect is suchthat if the retarder switch is turned on when braking is beingperformed, the control means selects, in accordance with the currentlyprevailing steering angle of the wheel, the control characteristic ofthe retarder braking force set in the map, and executes retardingcontrol in line with the set control characteristic in such a mannerthat the retarder braking force becomes relatively smaller the largerthe steering angle becomes.

When the currently prevailing slip rate, which has been computed inaccordance with the vehicle speed signal and driving-wheel velocitysignal, is in a predetermined range, namely when the coefficient offriction between a tire and the road surface lies within an effectiverange of coefficients of friction maintained above a predeterminedvalue, the control means outputs a retarder operating signal to theretarder actuating device so that the retarder braking force will bemaintained at a fixed value.

When the slip rate exceeds the predetermined range (the effective rangeof coefficients of friction), the control means outputs a retarderoperating signal to the retarder actuating device so that the retarderbraking force, with the result being that the slip rate is held in thepredetermined range (the effective range of coefficients of friction).

If the brake actuation signal is adopted as an ABS operating signal, theabove-described retarding control apparatus can be installed to functionin a vehicle equipped with an ABS (antiskid brake system). Even if avehicle is one not equipped with an ABS, the retarding control apparatuscan be installed if the brake actuation signal is adopted as the ONsignal of the brake switch attached to the brake pedal.

Thus, in accordance with the second aspect of the invention, theretarder braking force is automatically controlled based upon the sliprate and steering angle of the wheel. Control is carried out in such amanner that the retarder braking force becomes smaller the larger thesteering angle. When the slip rate becomes greater than a predeterminedvalue, control is performed in such a manner that the retarder brakingforce is reduced so that the slip rate will not exceed the predeterminedvalue. As a result, safe cornering of the vehicle becomes possible. Thisaspect of the invention is particularly effective for a large-sizevehicle.

In addition, the retarding control apparatus of this aspect of theinvention can be installed in both a vehicle equipped with an ABS and abehicle not having an ABS.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a retarding apparatus accordingto the prior art;

FIG. 2 is a block diagram illustrating a retarding apparatus accordingto another example of the prior art;

FIG. 3 is a diagram showing the relationship between coefficient offriction and slip rate;

FIG. 4 is a diagram showing characteristics of retarder braking forceaccording to the prior art;

FIG. 5 is a block diagram showing an embodiment of a first aspect of thepresent invention;

FIG. 6 is a graph showing amounts of braking force decrease in thisembodiment;

FIG. 7 is an explanatory view for describing control of retarder brakingforce in this embodiment;

FIG. 8 is a diagram showing the construction of an embodiment accordingto a second aspect of the present invention;

FIG. 9 is a flowchart for describing retarding control in thisembodiment; and

FIG. 10 is a map illustrating the characteristics of retarder brakingforce in this embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Aspect of the present invention will now be described in detailbased upon an embodiment illustrated in FIGS. 5 through 7.

As shown in FIG. 5, an electronic control unit ECU 21 comprising acomputer unit receives, as inputs thereto, a shift position signal αfrom a shift position sensor (shift position sensing means) 23 attachedto a shift lever 22, a throttle opening signal β from a throttle openingsensor (throttle opening detecting means) 24 attached to an acceleratorpedal, a vehicle speed signal γ from a vehicle speed sensor (vehiclespeed detecting means) 27 attached to an output shaft 26 of an automatictransmission 25, and a retarder changeover signal δ from a retarderchangeover switch 28. The ECU 21 outputs a retarder solenoid signal(current) I to a solenoid 30 connected to a control valve 29 forretarder control, therby controlling the operation of the control valve29 to regulate hydraulic pressure supplied to a hydraulic retarder 31attached to the output shaft 26 of the automatic transmission 25.

The ECU 21 is so designed that a manual downshift is decided when thefollowing two conditions are satisfied:

i) the throttle opening is zero, and

ii) the shift position of the shift lever 22 undergoes any of thechanges D →3, D →2, D →L, 3 →2, 3 →L, 2 →L.

When the retarder changeover switch 28 is turned on so that the retarderchangeover signal δ enters the ECU 21, the current I is delivered to thesolenoid 30 and hydraulic pressure is introduced to the retarder 31 byoperation of the control valve 29. As a result, a constant braking forceF₁ produced by the retarder 31 acts upon the output shaft 26.

If, when the retarder changeover switch 28 has been turned on so thatbraking is being performed by the retarder 31, as described above, theshift lever 22 is operated and the ECU 21 determines that a manualdownshift has taken place based upon the shift position signal α fromthe shift position sensor 23 and the throttle opening signal β from thethrottle opening sensor 24, then the ECU 21 reduces the braking force ofthe retarder 31 by a braking force ΔF set for every position of thedownshifted shift lever 22, as illustrated in FIG. 6. As a result, theoutput of current I to the solenoid is diminished by a current ΔTcommensurate with the braking force decrease ΔF. It should be noted thatthe braking force decrease ΔF is set so as to be larger the closer theshift position is to the low-speed side, as will be understood from FIG.6.

By way of example, if the shift position signal α indicates a D →3 shift[(a) in FIG. 7] in a state where the retarder changeover switch 28 is onand the throttle opening is zero, then the current I to the solenoid 30is is reduced by a current ΔI₃ [(b) in FIG. 7] corresponding to abraking force decrease ΔF₃ (see FIG. 6) [(c) in FIG. 7] commensuratewith the "3rd" position of the shift lever 22.

Accordingly, the braking force F which acts upon the vehicle at thistime is expressed by the following equation:

    F=F.sub.1 +F.sub.2 +F.sub.3 -ΔF.sub.3

where F₂ represents a braking force produced by a foot brake and F₃represents a braking force produced by engine braking which accompaniesa manual downshift.

A time T for reducing the current ΔI is set in proportion to thecurrently prevailing vehicle speed. More specifically, based upon thevehicle speed signal δ from the vehicle speed sensor 27, the ECU 21computes the time T in accordance with the equation

    T=a·N

where a represents a constant and N the rotational speed (=vehiclespeed) of the output shaft, reduces the current I to the solenoid 30 byΔI for the period of time T, and halts the decrease in current I whenthe time period T elapses.

With the retarding control apparatus described above, the rates ofchange in vehicle speed and deceleration, as indicated by the solidlines at (d) and (e) in FIG. 7, are gentler than in the prior artindicated by the dashed lines. As a result, transmission shock issignificantly reduced.

Second Aspect of the present invention will now be described in detailbased upon an embodiment shown in FIGS. 8 through 10.

As shown in FIG. 8, a vehicle speed sensor 42 is attached to a drivenwheel (front wheel) of a vehicle 41A, and a wheel speed sensor 43 isattached to a driving wheel (rear wheel) 41B of the vehicle. A steeringangle sensor 44 is attached to a steering portion of the driven wheel41A. Vehicle speed V detected by the vehicle speed sensor 42 and wheelspeed v detected by the wheel speed sensor 43 enter an ECU 45. Alsoinputted to the ECU 45 are a steering angle signal θ from the steeringangle sensor 44 and an ON signal ε from a retarder switch 46.

If the vehicle is equipped with an ABS, it is so arranged that an ABSoperating signal τ enters the ECU 45. If the vehicle is not equippedwith an ABS, the arrangement is such that an operating signal η from abrake switch 17, which is attached to the brake pedal, is inputted tothe ECU 45.

On the basis of these signals, the ECU 45 outputs a control signal(current) I to a retarder solenoid 48 to actuate a control valve 49,thereby controlling a hydraulic retarder 51 mounted on the output shaftof a transmission 50.

Control of the retarder 51 performed by the retarding control apparatusdescribed above will now be set forth while referring to the flowchartof FIG. 9.

As shown in FIG. 9, the ECU 45 determines at step (a) whether an ABS ison and its operating signal τ has entered if the vehicle is equippedwith an ABS, or whether the brake switch 47 is on and its operatingsignal η has entered (namely whether the brake pedal has been depressed)if the vehicle is not equipped with an ABS. If the ABS or brake switch47 is not on, then control is ended at step (b). If the ABS or brakeswitch 47 is on, then it is determined at the next step (c) whether theretarder switch 46 is on.

If the retarder switch 46 is not on, control is ended at step (c); if itis on, then the vehicle speed V, the speed v of the driving wheel 41Band the steering angle θ are detected at step (d) based upon thedetection signals from the vehicle speed sensor 42, wheel speed sensor43 and steering angle sensor 44.

On the basis of the detected value of the steering angle θ, the ECU 45decides at step (e) which characteristic line l corresponding to thesteering angle θ to use in the map A of FIG. 10, which illustrates therelationship between retarder braking force F and slip rate S. Thecharacteristic lines l indicate successively larger steering angles fromtop to bottom. In addition, regions I, II, III corresond to regions I,II, III of map B (FIG. 3) illustrating the relationship between thecoefficient of friction μ which is produced between the tire and theroad surface, and the slip rate S.

Further, on the basis of the detected values of vehicle speed V andwheel speed v, the ECU 45 computes the slip rate S of the tires at step(f) in accordance with the equation S =V-v/V , compares the computedvalue of slip rate S with the map B of FIG. 3 and determines at step (g)in which region of the map B the current slip rate S resides. Here theregion II between S₁ and S₂ indicates the effective range of the sliprate S of map P.

When the current slip rate S is found to be in the range of region I ofmap B at the decision step (g) regarding slip rate S. the retarderbraking force F is controlled at step (h) in accordance with the portionof the characteristic line l of map A, which has been selected by thedecision step (e), that is inside region I. When the current slip rate Sis found to be in the range of region II of map B, the retarder brakingforce F is controlled at step (i) in accordance with the portion of thecharacteristic line of map A that is inside region II. When the currentslip rate S is found to be in the range of region III of map B, theretarder braking force F is controlled at step (j) in accordance withthe postion of the characteristic line of map A that is inside regionIII.

More specifically, in region I of map A, the current value of thecontrol signal I from ECU 45 to the retarder solenoid 48 is reduced withan increase in the slip rate S to S₁, thereby diminishing the retarderbraking force F. In region II, the current value I of the control signalfrom ECU 45 to the retarder solenoid 48 is held constant when the sliprate S is between S₁ and S₂, thereby holding the retarder braking forceF at a constant value F_(oi) .

In the area III of map III, the current value of the control signal Ifrom ECU 45 to the retarder solenoid 48 is reduced with an increase inthe slip rate from S₂. since the slip rate S declines owing to adecrease in the retarder braking force F, the slip rate S returns toregion II. In actuality, the slip rate S hardly ever exceeds the maximumvalue S₂ of region II and does not significantly enter the portions ofthe characteristic lines l of map A that are inside region III.

Thus, the retarder braking force F is controlled based upon the sliprate S of a tire, and optimum control characteristic is selected by thesteering angle θ of a wheel. As a result, the tire slip rate S isconstantly maintained in the effective region x of the map B.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

What is claimed is:
 1. A retarding control apparatus for controllingoperation of a retarder, which is connected to an automatictransmission, by operating a retarder actuating device by manipulationof a retarder changeover switch, comprising:vehicle speed detectingmeans for detecting vehicle speed; driving-wheel velocity detectingmeans for detecting velocity of a driving wheel; steering angledetecting means for detecting steering angle of a wheel; brake actuationdetecting means for detecting actuation of a brake; and control means towhich are inputted a vehicle speed signal from said vehicle speeddetecting means, a driving-wheel velocity signal from said driving-wheelvelocity detection means, a steering angle signal from said steeringangle detection means, a brake actuation signal from said brakeactuation detecting means and an ON signal from the retarder changeoverswitch, for outputting a retarder operating signal to the retardingactuating device; said control means having a map in which controlcharacteristics are set such that when a slip rate of the wheel is notmore than a fixed value, a retarder braking force is reduced as the sliprate becomes larger; when the slip rate exceeds the fixed value and liesin a predetermined range, the retarder braking force is held at aconstant value; and when the slip rate exceeds the predetermined range,the retarder braking force is reduced as the slip rate becomes largerand is made relatively smaller as the steering angle of the wheel largerbecomes; wherein when the brake actuation signal and the ON signal fromthe changeover retarder switch are being inputted to said control means,said control means selects from the map, on the basis of the steeringangle signal, a control characteristic of the retarder braking forcecorresponding to the steering angle, computes the slip rate based uponthe vehicle speed signal and the driving-wheel velocity signal, andoutputs the retarder operating signal to the retarder actuating devicebased upon the computed slip rate and the selected controlcharacteristic of the retarder braking force.
 2. The control apparatusaccording to claim 1, wherein the brake actuation signal is an ABSactuation signal.
 3. The control apparatus according to claim 1, whereinthe brake actuation signal is an ON signal from a brake switch.
 4. Thecontrol apparatus according to claim 1, wherein said control meanscomprises an electronic control unit for processing the followingsteps:(1) determining characteristic curve based on the steering anglein the map, (2) computing the slip rate based upon the vehicle speedsignal and the driving-wheel velocity signal, (3) determining whetherthe computed slip rate at step (2) is within, below or above thepredetermined range, and (4) outputting a signal according to thedetermining step (3).